Flexible keyboard

ABSTRACT

A flexible data input device including a first textile layer and a second textile layer, which are arranged spaced apart from each other by a spacer. The spacer includes apertures delimiting the active zones of the data input device. The two textile layers are electroconductive in the active zones and a material with pressure-variable resistance is applied in the active zones, at least on one of the textile layers.

INTRODUCTION

The present invention relates in general to a flexible data input devicesuch as a flexible keyboard.

To make it easier to input data into pocket computers (PDAs), it ispossible to connect a portable alphanumeric keyboard to said pocketcomputer. These portable keyboards often comprise several rigid keyboardelements that are linked together by hinges, so that they can be foldedup. Such a keyboard is, for example, described in documentWO-A-00/60438.

To further reduce the stowed size of a keyboard, keyboards made oftextile material have been developed. Such a keyboard comprises firstand second electrically conductive textile layers that are placed acertain distance apart by means of a spacer fabric. The textile layersare, for example, woven or knitted using electrically conductive yarnsand insulating yarns. When an electrical voltage is applied between twoterminals of one of the layers, an electrical gradient is createdbetween the two terminals of the electrically conductive textile layer.When a force is exerted on one of the textile layers, the two layerscome into contact and the electrical voltage measured is representativeof the point of interaction of the force. A textile position detectorthat can be used as a keyboard is, for example, disclosed in documentEP-A-0 989 509.

A simple and inexpensive keyboard is produced in this manner that has ahigh degree of flexibility, for example allowing it to be wound aroundthe pocket computer. One disadvantage of such a keyboard is revealedwhen it is used on a curved surface. This is because, when the keyboardis curved the two electrically conductive textile layers easily toucheach other, without the user exerting an actuating force on one of thetextile layers. Since each contact between the layers is interpreted asan activation of a “key”, it follows that the data input is corrupted bysignals coming from an erroneous contact between the two electricallyconductive layers.

OBJECT OF THE INVENTION

The object of the present invention is to propose a flexible data inputdevice that considerably reduces the risk of any erroneous activation.

GENERAL DESCRIPTION OF THE INVENTION

This objective is achieved by a flexible data input device, comprising afirst textile layer and a second textile layer, said first and secondtextile layers being arranged a certain distance from each other bymeans of a spacer, said spacer having openings that define active areasof said data input device. In accordance with the invention, said firstand second textile layers are electrically conductive in said activeareas and a material exhibiting pressure-variable resistance is applied,in the active areas, on at least one of the textile layers. Thanks tothe material exhibiting pressure-variable resistance, the electricalresistance between the two textile layers varies with the pressureapplied between the two layers. This device therefore makes it possibleto define a pressure threshold above which a “key” defined by one of theactive areas of the device is considered to be actuated by a user.

The determination of the resistance between the two textile layers foreach active region, that is to say for each key, and the interpretationof this determination may be implemented by the pocket computer itselfor by an electrical circuit of an interface connected to said device.The threshold will be set so as to be able to distinguish between anaccidental contact between the two textile layers, caused by flexure ofthe device, and an intentional contact corresponding to the activationof one of the “keys”. For a low pressure, such as that when anaccidental contact between the two textile layers occurs, thisresistance threshold will not be exceeded and the contact is notinterpreted as the actuation of a key by a connected electronic circuit.

It should be noted that the variable-resistant material may equally wellbe a material whose internal resistance varies with pressure as amaterial whose surface resistance with the textile layers varies withpressure. In addition, the variable resistance may equally well increasewith pressure as decrease.

The role of the variable-resistance material is to be able todistinguish the electrical resistance between the two textile layerswhen an accidental contact occurs from that when a key is activated. Todo this, all that is required in general is to have a very thin layer ofthis material, above all in the case of a material whose variableresistance is based on the surface effect described above. Consequently,the flexibility of the device is barely affected by the application ofthis thin layer.

In one advantageous embodiment of the device, a material exhibitingpressure-variable resistance is applied, in the active areas, to each ofthe textile layers. This embodiment allows the thickness of the layersof variable-resistance material to be further reduced, while stillensuring good dynamic behaviour of the device.

The variable-resistant material, preferably a semiconductor material,may be easily applied to the textile layers by a screen-printing orspray method or by any other deposition method. It is then possible toapply it in the form of a continuous layer or else in the form of spotsspaced apart over said textile layer in question. In the second case,the space in between the various spots will be chosen to be small enoughnot to allow direct contact between the textile layers. Such aconfiguration with several spaced-apart spots exhibits betterflexibility compared to a continuous layer. Alternatively, and dependingon the method of deposition chosen, the variable-resistant material maybe applied in the form of microscopic granules. This embodiment ensuresmaximum flexibility of the keyboard.

The textile layers exhibit electrical conductivity at least in theactive areas. This electrical conductivity may, for example, be achievedby the incorporation of conductive fibres into said fabric. In apreferred embodiment of the device, said first and second textile layersinclude a metal coating in the region of said active areas. Thetechniques involved in depositing such a metal coating can be wellcontrolled and the fabrics can be produced at low cost. The appliedlayers are very thin and the flexibility of the fabric is entirelypreserved. In addition, the metallization techniques allow theelectrically conductive regions to be well delimited from the insulatingregions.

In a preferred version of the invention, the first textile layer and thesecond textile layer each have a metal coating in the form of adjacentbands, the textile layers being oriented so that said coatings in theform of bands intercept in the active areas of said device. Similarly, a“matrix” arrangement may be produced wherein the bands of the firsttextile layer constitute the columns and the bands of the second layerconstitute the rows. Thus, each active area, and therefore each key ofthe keyboard, is formed between a “column” band of the first textilelayer and a “row” band of the second textile layer. Such an arrangementadvantageously limits the number of connections needed to address thevarious active areas. This is because each active area may be monitoredby measuring the resistance between the two respective bands forming thekey.

It should be noted that such an arrangement also makes it easier toconnect the device, since the metallized bands lend themselves well tobeing crimped.

In an alternative version, the first textile layer has a continuousmetal coating and the second textile layer has a metal coating in theform of isolated sections localized at the points where the active areasare. In such an embodiment, the metal layer of the first textile layerconstitutes the common electrode for each of the active areas of thedevice. The isolated sections of the second textile layer must becontacted individually in this embodiment. The conductors used forcontacting the metal coatings are preferably deposited on the respectivetextile layer.

In both embodiments, it will be appreciated that the device comprisesdiscrete active areas whose resistance may be determined individually.Unlike the keyboards of the digitising tablet (XY pad) kind, such akeyboard allows multiple attribution of the keys by means of a “shift”key.

The spacer of the device comprises a compressible or noncompressiblewoven or nonwoven, depending on the use. It will be appreciated that, inan alternative version, the spacer comprises an insulating granulatedmaterial applied to one of the textile layers. In this case, theparticle size of the granulated material will be chosen so as to begreater than the thickness of the layer of variable-resistance materialor alternatively to the particle size of the granules ofvariable-resistance material.

The device may be assembled using several known techniques. For example,the textile layers are laminated to said spacer or else are stitchedthereto.

Description with the Aid of the Figures

Other particularities and features of the invention will emerge from thedetailed description of one advantageous embodiment presented below, asan illustration, with reference to FIG. 1 appended hereto. This FIG. 1shows a cross section through an active area of a flexible keyboard.

The keyboard 10 is formed by a first textile layer 12 and a secondtextile layer 14 that are placed a certain distance apart by means of aspacer 16. The spacer, which may be formed from a nonwoven, has openings18 that define an active area 20 of the keyboard. Within the active area20, each of the textile layers 12 and 14 is coated with a respectivethin metal layer 22 and 24. The metallizations 22 and 24 of the textilelayers 12 and 14 form the electrodes of the “key” defined by the activearea 20.

To prevent any accidental contact between the two electrodes by bendingthe keyboard, a material 26 and 28 exhibiting pressure-variableresistance is applied to the respective two metallizations 22 and 24.The material is applied, for example using a screen printing process, inthe form of spaced apart spots, the spacing between the spots beingsmall enough to avoid direct contact between the two metallizations.Thus, the flexibility of the textile layers is advantageously preserved.Alternatively, the variable-resistance material may be applied in theform of a continuous layer. Such an embodiment is shown by the dottedlines in FIG. 1.

1-14. (canceled)
 15. A flexible data input device, comprising: a firsttextile layer; and a second textile layer, said first and second textilelayers being arranged a certain distance apart from each other by aspacer, said spacer including openings that define active areas of thedata input device, wherein said first and second textile layers areelectrically conductive in the active areas, and wherein a materialexhibiting pressure-variable resistance is applied in the active areason at least one of said first and second textile layers.
 16. The deviceas claimed in claim 15, wherein the material exhibitingpressure-variable resistance is applied to each of said first and secondtextile layers in the active areas.
 17. The device as claimed in claim15, wherein the material exhibiting pressure-variable resistance isapplied in a form of a continuous layer on said at least one of saidfirst and second textile layers.
 18. The device as claimed in claim 15,wherein the material exhibiting pressure-variable resistance is appliedin a form of spaced-apart spots on said at least one of said first andsecond textile layers.
 19. The device as claimed in claim 15, whereinthe material exhibiting pressure-variable resistance is applied in aform of microscopic granules.
 20. The device as claimed in claim 15,wherein said first and second textile layers include a metal coating ina region of the active areas.
 21. The device as claimed in claim 15,wherein said first textile layer and said second textile layer each havea metal coating in a form of adjacent bands, said first and secondtextile layers being oriented so that said metal coatings in the form ofbands of said first textile layer and said second textile layerintersect in the active areas.
 22. The device as claimed in claim 15,wherein said first textile layer has a continuous metal coating and saidsecond textile layer has a metal coating in a form of isolated sectionsarranged at locations of the active areas.
 23. The device as claimed inclaim 15, wherein said spacer comprises a compressible woven or nonwovenmember.
 24. The device as claimed in claim 15, wherein said spacercomprises a noncompressible woven or nonwoven member.
 25. The device asclaimed in claim 15, wherein said spacer comprises a granulated materialapplied to one of said first and second textile layers.
 26. The deviceas claimed in claim 15, wherein said first and second textile layers arelaminated to said spacer.
 27. The device as claimed in claim 15, whereinsaid first and second textile layers are stitched to said spacer. 28.The device as claimed in claim 20, wherein conducting layers serving forcontacting the metal coatings are deposited on said first and secondtextile layers.
 29. The device as claimed in claim 16, wherein thematerial exhibiting pressure-variable resistance is applied in a form ofa continuous layer on said first and second textile layers.
 30. Thedevice as claimed in claim 16, wherein the material exhibitingpressure-variable resistance is applied in a form of spaced-apart spotson said first and second textile layers.
 31. The device as claimed inclaim 16, wherein the material exhibiting pressure-variable resistanceis applied in a form of microscopic granules.